1. Field of the Invention
The present invention relates to an image forming apparatus equipped with a lubricant application mechanism for applying a lubricant onto an image bearing member, such as a photosensitive drum or an intermediate transfer belt.
2. Description of the Related Art
Conventionally, an electrophotographic image forming apparatus, such as a copying machine or a printer, performs a process for image formation, including forming a toner image on an image bearing member, such as a photosensitive drum and an intermediate transfer belt, transferring the generated toner image on the image bearing member onto a sheet, and then fixing the toner image on the sheet to complete the image formation.
In such an image forming apparatus, not all toner of the toner image formed on the image bearing member, such as the intermediate transfer belt, is transferred onto a sheet, but a slight amount of toner which has not been transferred remains on the intermediate transfer belt. To positively remove foreign matters, including the above-mentioned remaining toner and paper powder which is attached from the sheet to the intermediate transfer belt during transfer of the image onto the sheet, the image forming apparatus is provided with a cleaning device for cleaning the intermediate transfer belt.
The cleaning device is configured to be brought into sliding contact with the intermediate transfer belt so as to eliminate powder remaining on the intermediate transfer belt, and hence there arises a problem of a frictional force acting between the cleaning device and the intermediate transfer belt. Further, when the cleaning device or the intermediate transfer belt deteriorates, the frictional force acting between the both increases to accelerate deterioration of the cleaning device and the intermediate transfer belt, whereby the frictional force further increases.
If the frictional force acting between the cleaning device and the intermediate transfer belt thus increases, abnormal noises may be generated from contact portions of the cleaning device and the intermediate transfer belt where the two are brought into contact with each other, and further, foreign matters may pass between the contact portions, which sometimes causes a cleaning failure.
To reduce the frictional force between the cleaning device and the intermediate transfer belt, the image forming apparatus is provided with a mechanism that applies a lubricant to the image bearing member, such as an intermediate transfer belt, and continuously performs lubricant application to thereby achieve reduction of the frictional force.
However, if the lubricant is excessively applied, the excessive amount of the lubricant cannot be scraped by the cleaning device, and as a result, part of the lubricant is conveyed up to a member, such as an electrostatic charger, and soils the member, which sometimes causes an image failure. To prevent such a problem, it is necessary to control the lubricant to a proper amount so as to prevent the lubricant from passing beyond the cleaning device, and soiling associated members, while reducing the frictional force.
That is, the image forming apparatus is required not only to apply a proper amount of the lubricant to the intermediate transfer belt, but also to prevent the lubricant from being excessively consumed, and an image failure from occurring, which is caused by adhesion of the excessive lubricant to the electrostatic charger.
A conventional image forming apparatus is configured such that a rotating lubricant application brush performs scraping of solid lubricant and application of the same to an image bearing member. Further, there has been proposed a technique in which the rotational speed of a lubricant application brush is properly changed according to the rotational speed of an image bearing member to thereby control the amount of applied lubricant to a proper amount (see e.g. Japanese Patent Laid-Open Publication No. 2010-096988).
When controlling the rotational speed of the lubricant application brush according to the traveling speed of the image bearing member as mentioned above, the lubricant is applied in an amount responsive to a change in the traveling speed of the image bearing member.
However, when the lubricant is applied in an amount responsive to a change in the traveling speed, it is not configured such that an actual excess or insufficiency of the lubricant is detected, and the lubricant is supplied according to the actual excess or insufficiency of the lubricant. Therefore, there sometimes occurs a case where an amount of the lubricant required according to the actual state of friction is not properly supplied between the cleaning device and the intermediate transfer belt.